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    <title>Document</title>
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<body>
    <script>
        //依次执行异步代码

        //依次执行
        function fn1() {
            return new Promise(resolve => {
                setTimeout(() => {
                    console.log(111);
                    resolve(1);
                }, 1000);
            })
        }

        function fn2() {
            return new Promise(resolve => {
                setTimeout(() => {
                    console.log(222);
                    resolve(2);
                }, 1000)
            });
        }

        function fn3() {
            return new Promise(resolve => {
                setTimeout(() => {
                    console.log(333);
                    resolve(3);
                }, 1000)
            })
        }

        //链式调用
        fn1().then(resolve => {
            console.log(resolve);
            return fn2();
        }).then(resolve => {
            console.log(resolve);
            return fn3();
        }).then(res => {
            console.log(res);
        })
    </script>
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